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2-in-1 device cleans sewage while generating electricity


March 29, 2012
By Anthony Capkun

March 28, 2012 – Scientists today described a new, more efficient version of a device the size of a home washing machine that uses bacteria growing in municipal sewage to make
electricity while simultaneously cleaning up the sewage.

Their report at the 243rd National Meeting & Exposition of the American Chemical Society (ACS) suggests that commercial versions of the 2-in-1 device could be a boon for the developing world and areas short of water.

“Our prototype incorporates innovations so that it can process five times more sewage six times more efficiently at half the cost of its predecessors,” said Orianna Bretschger, Ph.D., who presented a report on the improved technology at the ACS meeting. “That actually puts us in a realm where we could produce a meaningful amount of electricity if this technology is implemented commercially. Eventually, we could have wastewater treatment for free. That could mean availability for cleaner water in the developing world…”

Current wastewater treatment technology involves a number of steps designed to separate the solid and liquid components of sewage and clean the wastewater before it is released into a waterway. This often involves settling tanks, macerators that break down larger objects, membranes to filter particles, biological digestion steps and chemicals that kill harmful microbes.

Bretschger’s team at the J. Craig Venter Institute is developing one version of a so-called microbial fuel cell (MFC). Traditional fuel cells convert fuel directly into electricity without igniting the fuel. They react or combine hydrogen and oxygen, for instance, and produce electricity and drinkable water. MFCs are biological fuel cells: they use organic matter, such as the material in sewage, as fuel, and microbes break down the organic matter. In the process of doing so, the bacteria produce electrons.

The new MFC uses ordinary sewage obtained from a conventional sewage treatment plant. Microbes that exist naturally in the sewage produce electrons as they metabolize, or digest, organic material in the sludge. Bretschger found that microbes exist in the MFC community that might even break down potentially harmful pollutants like benzene and toluene that may be in the sludge.

An MFC consists of a sealed chamber in which the microbes grow in a film on an electrode, which receives their electrons. Meanwhile, positively-charged protons pass through a membrane to a second, unsealed container. In that container, microbes growing on another electrode combine oxygen with those protons and the electrons flowing as electricity from the electrode in the sealed chamber, producing water or other products like hydrogen peroxide.